Typically in a gravel pack completion, a sump packer is set in the wellbore and the formation is perforated. The perforating gun is removed and a gravel packing assembly is installed. Screens are part of this assembly as is a crossover tool. The crossover tool is secured to a production packer. The production packer is set and the crossover is configured in a manner so as to allow pumping gravel through the production packer and into the annular space outside the screens. Return fluid, less the deposited gravel, goes through the production screen and through a valve in a blank pipe in the screen, back through the crossover and out the annular space above the set production packer. A closing tool on a wash pipe in a concentric string closes the sliding sleeve valve(s) when the crossover tool is pulled at the conclusion of the gravel packing operation. After the production string is run to the production packer, access to the formation involved using wireline or service string through the production packer to shift the internally mounted sliding sleeve(s) to gain access to the producing formation. This technique is illustrated in U.S. Pat. No. 5,609,204 assigned to OSCA Inc. of Lafayette, La.
Subsequently, OSCA developed internally mounted pressure actuated circulating valves. These valves were integral to each section of screen assembly. Each screen section had a non-perforated base pipe having the sliding sleeve valve over a series of openings mounted on each screen section. For long screen intervals, numerous valves were required to be manipulated for full access to the producing zone. The close fit of these sliding sleeves to the screen and the integral construction did not allow for alternate access to the formation if such valves refused to open. Additionally, the integral construction with the screen sections precluded removal of such valves if they failed to operate without removing the entire screen assembly integral to such sliding sleeve valves. The presence of gravel exterior to the screens made it problematic to remove the screen assembly after deposition of the gravel.
Other commercially available systems from Schlumberger and Weatherford used isolation ball valve systems as opposed to concentric isolation string hookups.
The present invention seeks to address several limitations in the prior systems. It not only allows access to multiple zones with pressure actuated valves that open after pressure is applied and then removed, but it also allows through the use of a redundant valve, the ability to close off the access to a given layer should that be necessary, while maintaining the capability of re-accessing the zone at a later date. Should the main valves not open in response to application and removal of pressure, the annular gap to the screen allows for access through the blank pipe without damaging the screen. Additionally, by placing the access valves on a removable portion of the inner string, the invention permits removal of the access valve while leaving the screen and surrounding gravel pack in place. The use of this inner string, separate from the screen, also permits the use of systems which manipulate the entire concentric string itself in order to provide alternate flow paths during packing operations. These and other benefits of the invention will become clearer to those skilled in the art from a review of the description of the preferred embodiment and the claims, which appear below.